The invention relates generally to color copying.
More particularly, the invention relates to a method of and an apparatus for determining the amounts of blue, green and red copy light required to reproduce a colored original on color copy material.
In order to determine the amounts of blue, green and red copy light required for reproduction of a colored original, the blue, green and red densities of the original are measured. It is generally attempted to adjust the spectral sensitivities of the density measuring system as closely as possible to the spectral sensitivities of the copy material. This is done so that the original may, during the measurement procedure, be evaluated with the "eyes" of the copy material, so to speak.
The U.S. Pat. No. 4,589,766 teaches that mixed production, i.e., the copying of different types of film, may be carried out with a single memory when measurement of the color densities of the films is performed under conditions which allow the spectral sensitivities of the copy material to be approximated as closely as possible. The spectral transmissivity curves of the color filters disposed in front of the measuring cells are here calculated step-by-step as a function of wavelength based on the existing physical magnitudes. These curves are subsequently attained by vapor depositing absorption layers of different thickness on the filter carriers. In this manner, optimal adjustment of the measuring system to the spectral sensitivities of the copy material is achieved taking into account non-uniformity in the spectral sensitivities of the measuring cells and differing spectral absorption characteristics in the measuring and copying color channels.
The preceding filter production technique is exceedingly complicated. Moreover, it is difficult to regulate with the required accuracy, especially when there are small variations in the spectral sensitivities of the copy material.